Electromagnetic relay operation monitor

ABSTRACT

A monitoring circuit is disclosed that is connected to the driving conductor to the relay by a transformer having one winding in series with the drive line from a fast operating, electronic, common control sequencing circuit. The monitor circuit includes a transistor, connected to another winding of the transformer and normally biased to be nonconductive. The transistor is brought into its conductive state by the dip in the operating current flowing in the drive conductor as sensed by the transistor to set a bistable device to record the operation of the relay.

United States Patent Wedmore 1 July 18, 1972 54] ELECTROMAGNETIC RELAY3,275,899 9/1966 Wolf ..317/DIG. 6

OPERATION MONITOR Primary Examiner-L. T. Hix [72] Inventor Williamwedmore Glen Ellyn Attorney-K. Mullerheim, B. E. Franz and Theodore C.Jay, [73] Assignee: GTE Automatic Electric Laboratories ln-' corporated,Northlake, Ill. 22 Filed: Feb. 25, 1971 [57] ABSHMCT [2]] Appl No:118,717 monitoring circuit is disclosed that is connected to the drivmgconductor to the relay by a transformer having one winding in serieswith the drive line from a fast operating, elec- Cl ..3l7/l37, 340/248R, 3 5 tronic, common control sequencing circuit. The monitor cir- [51]Int. Cl. ..H0lh 47/00 cuit indudes a transistor, connected to anotherwinding f the [58] Field ot'Search ..317/l37, 148.5 R, DIG. 4, DIG. 6;transformer and normally i d to be nonconductive The 340/248 Rtransistor is brought into its conductive state by the dip in the Ioperating current flowing in the drive conductor as sensed by [56]References Cited the transistor to set a bistable device to record theoperation UNITED STATES PATENTS of the y- 2,994,07l 7/1961 Olson et al...317/DIG. 6 1 Claim, 2 Drawing Figures RELAY MATRIX rl siesta 2;ssiiiccifis J5 E |7 L l2 t r|8 PATENTEU JUL] 81972 3,678,344

RELAY MATRIX GATING 3O SIGNAL 22 CONTROL CLEAR R 0gb 2O CIRCUIT 7 FIG.

32 9,15 L F/G. 20

FIG. 2b

RELAY ARMATURE MOTION F/G. 2c

0 A F/G. 2d

F/G. 2e

INVENTOR WILLIAM R, WEDMORE ATTORNEY BACKGROUND OF THE INVENTION 1.Field of the Invention This invention pertains to circuits formonitoring the operation of electromagnetic relays.

2. Description of the Prior Art In electronically controlled circuitsfor operating relays in a switching system, commands for operatingrelays are to be given successively as rapidly as possible in order toprovide the most economical use of the system. To complete a sequence ofinterdependent relay operations, where it is necessary that a certainrelay or relays be operated before the command for a subsequent relay tooperate be given, it is essential that the sequencing control provideample time for the operation of the preconditioning relays prior toapplying the subsequent operating command. When a fixed time interval isprovided, it must be sufficient for the slowest operating relay of itstype to operate completely. This interval must be sufficient for eventhe most adverse condition. An interval longer than required would ofcourse slow down the system, while a shorter interval would obviouslynot insure that every relay could operate within the allotted time.Further, this time interval that must be provided for the relayoperations while small, is cumulative in a system where many relays maybe required to operate in sequence.

SUMIVIARY OF THE INVENTION Accordingly it is an object of this inventionto provide an improved circuit for determining when a relay hasoperated.

This is accomplished by sensing the change in current in a drive line tothe relay. Use is made of a characteristic possessed by relays employingmoving armatures, that is, as the armature moves toward the relay polepiece it generates a counter electromotive force that causes a sharpreduction in the current flowing in the relay winding. This effectpersists for as long as the armature is in motion, typically more than 1millisecond. It is also evident during the time that a relay isreleasing as the armature is moving away from the relay pole piece.

By using the usual windings of the relays for the critical timingpurposes, a minimal number of additional circuitry and parts arerequired. The time interval allotted for the operation of a particularrelay is variable and determined by the relay itself. The circuitautomatically adjusts the interval to the differences in thecharacteristics of different relays that may be connected to thiscircuit and for the different rates of operation or release that may becaused by external parameters.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a generalized black and linediagram of a circuit embodying the principles of this invention;

FIG. 2 shows a series of waveforms at various points in the diagram ofFIG. 1 to assist in an understanding of the operation of the circuit.

DESCRIPTION OF THE PREFERRED EMBODINIENT In FIG. 1 relays l1, 12, 13 and14 represent a number of relays in a relay matrix group that areselectively operated as required by the closing of their operate pathsat the select switches l5, l6, l7 and 18 from a source of positivepotential at terminal 19 to a negative potential at terminal 20. Atransformer 21 has a winding 22 located in series in the drive line tothe relay coils. The other winding 23 of this transformer is connectedbetween the negative potential 20 and the base of transistor 25 viaresistor 24. Transistor 25 has its emitter connected to the negativepotential source 20, and its collector to a positive potential source19' via resistor 26. In this configuration the transistor is normallynon-conductive, and remains so during the time that the current flowsthrough winding 22 to energize the selected relay, since winding 23 ispolarized to cause a negative bias upon the base of transistor 25 duringthe current build up interval. This invention makes use of acharacteristic possessed by relays employing moving armatures, that is,as the armature moves toward the relay pole piece it generates a counterelectromotive-force that causes a sharp reduction in the current risingin the relay winding. This effect persists for as long as the armatureis in motion and is illustrated in FIG. 2( b). The voltage to the baseof transistor 25 varies as shown by FIG. 2(0), where the increase ofnegative bias can be seen up to the point that the relay armature startsto move. At this time the voltage swings in the positive direction, andreaches a value sufficient to cause a current flow from terminal 19'through resistor 26 through the collector to emitter path of transistor25 to the negative source terminal 20 as shown by FIG. 2(d). The voltageat terminal 30 swings from the nominal value at source 19' into thenegative direction as shown by FIG. 2(e).

The switches 15, I6, 17 and 18 are controlled by a common controlcircuit 29 which also serves to sequence other operations within thesystem of which relays 11 through 14 are a part of. This control circuit29 prior to the time of operation of the selected switches, restsbistable register 28 and immediately after operation of the selectedswitches applies a gate signal to AND gate 27. As can be seen from FIG.2(a), the duration of the gate signal is for an interval suflicient forthe selected relay to fully operate under worse case conditions. Gate 27is now primed and upon detection of the pulse from transistor 25,indicating the operation of the relay, a set pulse will be passed to theinput of the bistable register 28. The set output at the l terminal nowserves to trigger the control circuit 29 to proceed with any followingsteps of the sequence without waiting the fully interval of the gatesignal pulse.

What is claimed is:-

I. In a system having a plurality of electromagnetic relays withrespective inductive coils and armatures, a control circuit common toall of said relays, a source of energizing potential, a plurality ofcurrent paths from said source of potential through said relay coils,and switching means in said current path controlled by said controlcircuit for selectively completing said current paths for controllingselected ones of said relays; the improvement comprising a monitorcircuit for providing an indication of the operation of said selectedrelays to said control circuit comprising: a transformer having a firstand a second winding, said transformer first winding connected in saidcurrent path, a transistor having a base, emitter and collector, saidcollector and emitter operatively connected to said source of energizingpotential, said transformer second winding connected to said transistorbase and emitter, said transformer windings poled to bias saidtransistor into a non-conducting direction upon said switching meanscontrolling said relay to operate it, a two input AND gate having afirst input connected to said transistor collector and a second inputconnected to said control circuit, said second input energized by saidcontrol circuit upon said control circuit controlling said selectingmeans to complete a circuit path to a selected one of said relays,bistable register means having a set input connected to said gate outputand a set output connected to said control circuit, said transformer andsaid transistor responsive to the induced voltage pulse appearing acrosssaid relay coil while said relay armature is in motion for generating apulse at said transistor collector terminal, said gate operatedresponsive to said pulse to set said register, whereby said registeroutput is sent to said control circuit to trigger a following operation.

1. In a system having a plurality of electromagnetic relays withrespective inductive coils and armatures, a control circuit common toall of said relays, a source of energizing potential, a plurality ofcurrent paths from said source of potential through said relay coils,and switching means in said current path controlled by said controlcircuit for selectively completing said current paths for controllingselected ones of said relays; the improvement comprising a monitorcircuit for providing an indication of the operation of said selectedrelays to said control circuit comprising: a transformer having a firstand a second winding, said transformer first winding connected in saidcurrent path, a transistor having a base, emitter and collector, saidcollector and emitter operatively connected to said source of energizingpotential, said transformer second winding connected to said transistorbase and emitter, said transformer windings poled to bias saidtransistor into a non-conducting direction upon said switching meanscontrolling said relay to operate it, a two input AND gate Having afirst input connected to said transistor collector and a second inputconnected to said control circuit, said second input energized by saidcontrol circuit upon said control circuit controlling said selectingmeans to complete a circuit path to a selected one of said relays,bistable register means having a set input connected to said gate outputand a set output connected to said control circuit, said transformer andsaid transistor responsive to the induced voltage pulse appearing acrosssaid relay coil while said relay armature is in motion for generating apulse at said transistor collector terminal, said gate operatedresponsive to said pulse to set said register, whereby said registeroutput is sent to said control circuit to trigger a following operation.